Many amplifier and speaker systems provide reasonably good quality sound reproduction at volumes below a volume distortion threshold, while providing badly distorted sound at volumes significantly above the volume distortion threshold.
Distortion above the volume distortion threshold may be caused by amplifier clipping or saturation, as well as nonlinearities in the speakers themselves. For example, while many speakers have speaker-cone suspension systems that act like nearly-linear springs for small cone displacements, at large cone displacements return forces are nonlinear, being stronger than would be expected of a linear spring. Other nonlinearities result from changes in inductance as the voice coil moves through the magnetic field of the speaker, and changes in speaker compartment volume as the speaker cone moves. Yet more nonlinearities result from loose or failed glue, rubbing speaker parts, dirt, and other age-related effects.
Speaker housings, which often double as housings for other electronics from cell phones, televisions, computers, or intercoms, may also introduce nonlinearities at high volume as housing parts and housing contents vibrate, including vibrating against each other.
All these nonlinearities in amplifier and speaker result in amplifier-speaker system distortion.
Speaker distortion often includes harmonic distortion, where second and third harmonics of large signals appear. In addition to harmonics, speaker distortion may also include intermodulation products, where a first and second input frequency mix to generate sum and difference frequencies in speaker output. Many people can hear these harmonics and intermodulation products, finding them objectionable and finding they impair speech intelligibility.
Speaker system distortion at high volumes can be reduced by using larger, higher-power, speaker systems with higher distortion thresholds—this raises cost of systems.
Apparent speaker system distortion can also be reduced by use of dynamic compression, where loud signals are detected and volume automatically reduced. Such systems typically require careful engineering of compression parameters for each speaker system, amplifier, and application.